Inside Texas Tech: A Stellar Collision

A Texas Tech physicist found out this summer just how patient she is. After gravitational waves were for the first time observed from the collision of two neutron stars, she kept collecting data waiting for a discovery she was seeking. The end result for scientists around the world was getting to see and hear two dead stars collide in a distant galaxy.

Texas Tech physicist Alessandra Corsi learned of the first-ever gravitational wave signal from a collision of two neutrons stars August 17 when an observatory in the US detected it. Gravitational waves had been detected four previous times but those happened when black holes merged.

Notification sped to scientists worldwide and various types of telescopes turned skyward to gather data from the collision that occurred 130 million light years away.

A mere 1.7 seconds after the gravitational wave was detected, gamma rays dimmer than usually seen were recorded. Hours later, scientists detected ultraviolet, visible and infrared light from the smashing neutron stars. Nine days later, X-rays showed up.

It was 16 days after the gravitational wave signal was detected that Corsi and a scientist at the California Institute of Technology independently confirmed radio waves from the collision’s jet of fast-moving material. As this jet slows down and expands, X-rays and very high frequency radio waves are also emitted in what’s known as ‘afterglow.’

Corsi says the jet shocked the interstellar medium -- the gas and dust between stars – and gave rise to the radio emission.

“It was a rather faint glow at the beginning when it just turned on,” Corsi says. “So the fact that we could both find the frequencies and we both saw it analyzing data independently, was a huge confirmation for us. So we finally said, alright we’ve got it and we decided to issue the detections and then worked together to continue monitoring the source.”

Because it took so long to detect the radio waves, Corsi knew this collision was providing a new point of view. The view of the collision was like seeing light from a flashlight while standing to its side. This explained why the gamma ray burst was dimmer than those seen before. “It took a bit for that bit to accelerate and reach our eyes,” she says.

The messengers - the optical-infrared emission and X-rays and radio – provide complementary information to help create the most complete picture of the entire event. Gravitational waves convey strong gravity. And light is needed to see the material that was spit out from the collision – how the gold and platinum are created.

Benjamin Owen, a Texas Tech physics professor and Corsi’s colleague, also worked on this discovery. He focused primarily on the structure of the neutron stars through the tidal effects on gravitational waves produced in the collision.

Gravitational waves were detected by the Laser Interferometer Gravitational-Wave Observatory, known as LIGO. Its founders won the Nobel Prize in Physics less than two weeks before the discovery. Corsi said timing was on scientists’ side.

“We would probably have gotten this a few years down the road so it was just incredibly amazing to get everything with this event right towards the end of LIGO second observing run. The detectors were about to be switched off and at the end we got this excitement. It was incredible,” she says.

Corsi says the discovery will change astronomy going forward. “You can think about as a totally different way now of doing astronomy,” she says. “Before you were limited to a picture, maybe a black and white picture of this explosion, and now you’re seeing it in 3D and from experiencing that collision with all possible senses.”